1. Field of the Invention
The present invention relates to a hydraulic clamp adapted to press and fix a fixed object such as a metal mould, a work pallet and the like onto a fixing table of a manufacturing machine such as an injection moulding machine, a machining center and so on, and more specifically to a hydraulic clamp of the type in which a clamping-member is linearly actuated by means of a hydraulic piston.
2. Prior Art
As such a hydraulic clamp, there has been provided the one illustrated in FIGS. 6 and 7, which is known by the inventor of the present invention and is constructed as follows.
A housing 104 of a hydraulic clamp 103 is formed in a horizontalized U-like configuration, while a cylinder bore 111 and a spring accommodation bore 121 are vertically formed in an overhang portion 140 of its front upper portion. A piston 113 is so inserted into the cylinder bore 111 so as to be slidable in an oil-tight manner in the vertical direction. A clamping actuation oil chamber 115 is formed above the piston 113 within the cylinder bore 111. A clamping-member 105 projects downwardly from the piston 113. An unclamping spring 123 is mounted externally around the clamping-member 105 within the spring accommodation bore 121. When the piston 113 is actuated downwardly by means of a hydraulic pressure within the clamping actuation oil chamber 115, the clamping-member 105 serves to press and fix a fixed portion 102a of the metal mould 102 from above.
There are, however, the following problems associated with the above-mentioned prior art.
(a) In order to make the housing 104 sufficiently bearable against a clamping reaction force transmitted to the overhang portion 140 from the clamping-member 105, it is necessary to increase a rigidity of a column portion 141. As a result, the housing 104 needs to be made larger in dimension and heavier in weight.
(b) Since a height dimension of the cylinder bore 111 is limited by a height dimension of the spring accommodation bore 121, an allowed stroke S of the piston 113 must be short. Therefore, an adjustable range R of a clamping thickness obtained by subtracting a minimum clamping thickness t from a maximum clamping thickness T is small.